Bambi does it for the baby boomers. Heidi has fiftysomethings reaching for their hankies. Rescreen ET for a 35-year-old and there will be tears before bedtime. But for anyone at the tail end of their 20s, chances are their first experience of sobbing at the cinema was four-fifths of the way through My Girl. Directed by the late Howard Zieff in 1991, My Girl told the story of 11-year-old Vada Sultenfuss (Anna Chlumsky), a cynical hypochondriac with a dead mum, funeral director father (Dan Aykroyd), senile granny, hostile classmates and sorrowful crush on English teacher Griffin Dunne. One summer, her prospects brighten after she finds tentative first love with boy next door Macaulay Culkin - until a bee attack puts him, too, on dad's mortuary slab.

Watch it today and My Girl has lost little of its power to upset. It plays out like tweenie Thomas Hardy - alternately bucolic and horrific, its heroine plagued by crushing bad luck. At the time of release, attention centred on Culkin - fresh from slapstick success in Home Alone, and just at the start of his slide into child-star hell (divorcing parents, befriending Jacko). But with hindsight it is Chlumsky who seems the real find - direct, charming and deadpan funny.

And then? Not much. My Girl 2, in which Vada is helped over her grief by a charmless skateboard enthusiast, didn't help cement a reputation. And few can remember Gold Diggers: The Secret of Bear Mountain - the gal-pal flick she made with Christina Ricci.

But now, 17 years after My Girl, Chlumsky's big smiley head has popped up again, this time in a thoroughly adult arena. In the Loop, Armando Iannucci's film based on The Thick of It satirising the backstage wrangles leading to the 2003 Iraq invasion, stars Mimi Kennedy as an embattled US "secretary of diplomacy" facing off against her inept UK opposite, Tom Hollander, plus Peter Capaldi's exotically blasphemous spin doctor Malcolm Tucker. Chlumsky plays Kennedy's aide, Liza: efficient, good-hearted, and, briefly, the bedfellow of Hollander's smitten assistant (Chris Addison). Much of the film jabs at British politicians' knee-jerk crush on Washington: the pomp and the limos, the power and the confidence.

Chlumsky, now 28, with a degree in international relations and married to a soldier named Shaun So, claims to be unaware of the phenomenon. "It was a real surprise," she says on the line from Rhode Island. "For me it's always been the other way round." Really? "Yeah! You guys can say the stupidest thing but that accent will turn me to jelly."

Travelling the world after college, she failed to notice any cultural enthral towards America - quite the opposite. "I could see why you might pretend to be Canadian - there was a certain bristle you'd prepare yourself for."

Given her husband's line of work - he has served in Afghanistan - did she find playing a professional pacificist difficult? "Well, Shaun says - and I agree with him - that war sucks, no matter if it's now or in the Iliad. But I do think it is easier to see why they were out there [Afghanistan] than in Iraq."

Much is made in the film of Americans' appalled reactions to Tucker's stream of obscenities. How about the language - did that trouble her? She laughs. "I struggled with the sexual content. Not that I find cursing offensive -I can sailor it up with the best of them - but these lines are just so graphic you can't help but picture what's being described."

Chlumsky seems unnervingly balanced - friendly, fun and astute. How has she turned out so normal? It's hard not to suspect that her relative failure - that early career dry spell, at least - must have helped. "I was fortunate not to be waylaid," she says, choosing her words carefully. "It was difficult because the fans were my own age and at that age, you can't properly articulate your feelings. As a child you want to be approved of, and if you're not getting parts because you're too fat, that's hard to properly understand.

"But everyone goes through a time when they don't know how to value themselves. It's good to have had a little bit of trauma. Also, if not, everyone would just hate you! And I'd rather have been a bit unhappy than be ostracised by society. That's a good trade off."

Charles Gant: Armando Iannucci's film converted its critical acclaim into a solid opening at the weekend, one of the films that helped the UK box office to a healthy 47% rise over the same period last year